I. Field
The following description relates generally to communication systems, and more particularly to a method and apparatus for soft symbol determination.
II. Background
In wireless communication systems, symbols are communicated between wireless devices to maximize information transmission. As part of the error detection and correction process for symbol transmission, a cyclic redundancy check (CRC) process is used to detect accidental changes to raw data. In the CRC process, a short, fixed-length binary sequence is calculated. This sequence is known as the CRC code or simply CRC. When a block is read or received the device repeats the calculation; if the new CRC does not match the one calculated earlier, then the block contains a data error and the device may take corrective action such as rereading or requesting the block be sent again. Interference cancellation may be then used to remove interference when the CRC passes.
In practice, CRC does not pass 10-30% of the time. In these cases, it is still desirable to use the information to remove interference. One approach involves using iterative and soft-interference schemes, which can provide 1-2+dB gain depending on the scenario. In order to do iterative decoding of any type, a posteriori probabilities of the symbols after processing (e.g., turbo decoding) must be computed. In these schemes, the probability of the bits is an important quantity. In particular, the availability of the probability of the bits following a decoding or equalization event is desirable. Traditional data sequences are punctured and thus, some mechanism must be used to calculate these parity bit log-likelihood ratios (LLR) and also convert this information into symbol probabilities. Typically, a soft symbol re-encoder may be used. However, this element typically requires a design with some complexity.
Additional complexities are introduced when these decoding systems need to be applied to more sophisticated wireless communication schemes. For example, in order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input or Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for the next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
Consequently, it would be desirable to address some of the issues noted above.